(Meth)acrylic acid is generally prepared by gas phase oxidation of propane, propylene, (meth)acrolein, and the like in the presence of a catalyst. For example, propane, propylene, and the like are converted to (meth)acrylic acid through (meth)acrolein by gas phase oxidation in the presence of an appropriate catalyst in a reactor, and a reaction product mixed gas including (meth)acrylic acid, non-reacted propane or propylene, (meth)acrolein, inert gas, carbon dioxide, water vapor, and various organic by-products (acetic acid, high boiling point by-products, and the like) is obtained in the back end of the reactor.
As shown in FIG. 1, the reaction product mixed gas contacts water in an absorption tower (102), soluble gas is obtained as a (meth)acrylic acid aqueous solution together with water, and non-soluble gas is discharged to the top of the absorption tower and recycled to the gas phase oxidation reactor, or converted to harmless gas through an incinerator and discharged.
Also, the (meth)acrylic acid aqueous solution is supplied to a distillation tower (105), which is a water separation tower, and high concentration (meth)acrylic acid is obtained at the bottom of the distillation tower. In the distillation tower (105), azeotropic distillation is mainly used, wherein water is separated using a solvent that forms an azeotrope with water. Herein, the operation method of a separation column of the back end, the treatment method of separated water, and the like are significantly varied according to the selection of an azeotropic solvent.
For example, if a hydrophilic azeotropic solvent such as methylisobutylketone (MIBK) is used as the azeotropic solvent of the distillation tower (105), azeotropic removal of acetic acid may be difficult, only water may be removed in the distillation tower (105), and (meth)acrylic acid containing a large amount of acetic acid is recovered from the bottom of the distillation tower (105). Thus, to remove acetic acid, a low boiling point separation tower (107) and an acetic acid separation tower (109) are required, and finally, after passing through a high boiling point separation tower (108), crude (meth)acrylic acid is recovered.
For another example, as shown in FIG. 2, if a hydrophobic azeotropic solvent such as toluene is used as the azeotropic solvent of the distillation tower (105), main by-products of acetic acid form an azeotrope together with water and are recovered at one time. Thus, the purification steps in the low boiling point separation tower (107) and acetic acid separation tower (109) in FIG. 1 may be dispensed with, nearly pure (meth)acrylic acid is obtained together with high boiling point by-products at the bottom of the distillation tower (105), and subsequently, after passing through the high boiling point separation tower (108) for removing the high boiling point by-products, crude (meth)acrylic acid may be recovered.
Particularly, in Korean Published Application No. 2009-0041355, the inventors have suggested a method of reducing waste water amount and effectively inhibiting inflow of organics in a reactor, by circulating acetic acid-containing waste water that is generated from the top of the distillation tower(105) if a hydrophobic azeotropic solvent is used to the (meth)acrylic acid absorption tower(102) and reusing it.
However, although the method may achieve the effect of simplifying subsequent purification steps by using a hydrophobic azeotropic solvent, high temperature (meth)acrylic acid-containing gas should be still cooled, absorbed, and redistilled, and in the subsequent purification step, a high boiling point distillation tower (108) should be operated. Thereby, the energy consumption amount of the overall process increases, and problems such as polymer production in the distillation tower (105) due to the high boiling point by-products still exist.